A robust screening method for dietary agents that activate tumour-suppressor microRNAs

Certain dietary agents, such as natural products, have been reported to show anti-cancer effects. However, the underlying mechanisms of these substances in human cancer remain unclear. We recently found that resveratrol exerts an anti-cancer effect by upregulating tumour-suppressor microRNAs (miRNAs). In the current study, we aimed to identify new dietary products that have the ability to activate tumour-suppressor miRNAs and that therefore may serve as novel tools for the prevention and treatment of human cancers. We describe the generation and use of an original screening system based on a luciferase-based reporter vector for monitoring miR-200c tumour-suppressor activity. By screening a library containing 139 natural substances, three natural compounds — enoxolone, magnolol and palmatine chloride — were identified as being capable of inducing miR-200c expression in breast cancer cells at 10 μM. Moreover, these molecules suppressed the invasiveness of breast cancer cells in vitro. Next, we identified a molecular pathway by which the increased expression of miR-200c induced by natural substances led to ZEB1 inhibition and E-cadherin induction. These results indicate that our method is a valuable tool for a fast identification of natural molecules that exhibit tumour-suppressor activity in human cancer through miRNA activation.